1. Field of the Invention
The present invention relates to a broadcast communication method in a mobile communication system, a mobile communication system and a mobile station using the broadcast communication method.
2. Description of the Related Art
Conventional broadcast communication methods can be divided broadly into two kinds. The first method is a method in which it is insured perfectly that mobile stations receive broadcast information. According to the first method, every mobile station which is an object for broadcast communication sends ACK (acknowledgment) to a base station network every time the mobile station receives broadcast information. The base station network resends the broadcast information to a mobile station, if the mobile station does not send ACK. Examples which use this method are a broadcast service of a two way pager and the like. The base station network means a mobile communication system except for mobile stations in this specification.
The second method is a method in which it is not insured that mobile stations receive broadcast information. According to the second method, the base station network only sends broadcast information to mobile stations and any mobile station does not reply to the base station network. An example which uses this method is a broadcast service of a general pager.
According to the above-mentioned first method, the mobile stations can receive broadcast information almost perfectly. Thus, reliability is high. However, there is a problem that transmission efficiency is lowered since replies from mobile stations are concentrated. In addition, even when communication state is good, the base station network should prepare for receiving replies from all mobile stations. Thus, the mobile communication system operates inefficiently since the base station network must use unnecessary frequency resources. These problems become outstanding as the number of mobile stations increases.
According to the second method, there is no problem as to efficiency since the base station network only sends information. However, reliability is low since it is not possible to check whether a mobile station receives the information.
It is an object of the present invention to provide an efficient and reliable broadcast communication method in a mobile communication system.
The above object of the present invention is achieved by a broadcast communication method for a plurality of mobile stations belonging to a certain group in a mobile communication system, the broadcast communication method comprising the steps of:
a base station network in the mobile communication system sending information on broadcast communication to the plurality of mobile stations at a predetermined time; and
a mobile station in the plurality of mobile stations which does not receive the information or broadcast information of the broadcast communication inquiring of the base station network about the broadcast communication.
In the above-mentioned method, the information on the broadcast communication may include the time for performing the broadcast communication and a number indicating the group.
In the above-mentioned method, the base station network may perform the broadcast communication a plurality of times, and may send information which indicates that the base station network performed the broadcast communication to the group at a predetermined time after the broadcast communication.
The above object of the present invention is also achieved by a mobile communication system which performs broadcast communication for a plurality of mobile stations belonging to a group, the mobile communication system comprising:
a base station network including a part which sends information on broadcast communication to the plurality of mobile stations at a predetermined time;
a mobile station including a part which receives the information and receives broadcast information of the broadcast communication on the basis of the information; and
wherein the mobile station inquires of the base station network about the broadcast communication when the mobile station does not receive the information or the broadcast information.
In the above-mentioned system, the base station network may further include a part which performs the broadcast communication a plurality of times.
In addition, in the above-mentioned system, the base station network may further include a part which sends information which indicates that the base station network performed the broadcast communication to the group at a predetermined time after the broadcast communication.
The above object of the present invention is also achieved by a mobile station in a mobile communication system which performs broadcast communication, the mobile station comprising:
a part which receives information on the broadcast communication and receives broadcast information of the broadcast communication on the basis of the information;
a part which inquires of a base station network in the mobile communication system about the broadcast communication when the mobile station does not receive the information or the broadcast information.
In the above-mentioned mobile station, the information on the broadcast communication may include the time for performing the broadcast communication and a number indicating the group to which the mobile station belongs.
According to the above-mentioned invention, the base station network sends information such as the program table to the mobile station beforehand and the mobile station requests the broadcast information only when the mobile station did not receive the broadcast information. Therefore, transmission efficiency is not lowered in contrast to the conventional technique in which transmission efficiency is lowered due to ACK concentration. In addition, even when the mobile station could not receive the broadcast information, the mobile station can send a request for resending the broadcast information by receiving and checking information on broadcast communication such as the program table. Therefore, the mobile station can receive the broadcast information reliably. Thus, reliability increases.
In addition, according to the present invention, since the broadcast information may be sent a plurality of times, reliability is further improved.
Further, according to the present invention, when the mobile station could not receive the program table and the broadcast information, the mobile station can request the broadcast information since the base station network sends, at a predetermined time, information indicating that the broadcast information was sent. Therefore, reliability is further improved.